This invention relates to tetrahydrophthalic anhydride and a method for bulk transportation thereof for ultimate utilization in the preparation of tetrahydrophthalic anhydride-diol polysters.
Tetrahydrophthalic anhydride (THPA) which is used in preparing high quality polyesters is normally shipped and stored in the form of flakes. The THPA flakes are normally white; however, on reheating for use in the preparation of polyesters, the material discolors. It is believed that the discoloration may be due to the formation of peroxides when the THPA is contacted with air, either during or after the formation of the flakes. Attempts to overcome this problem by maintaining the THPA in a molten state from production to use have not been successful. The THPA turns brown, apparently by decomposition, if maintained at temperatures above its melting point (e.g., above about 105.degree. C.) for any substantial period of time, such as several days to several weeks, as would be encountered in the normal course of use.
It is an object of the present invention to provide a method of preparing tetrahydrophthalic anhydride in a form for storage and shipment, and for use in the preparation of polymers containing THPA and a diol. Another object of the present invention is to provide a method for preventing color degradation of THPA. It is an advantage of the present invention that the THPA may be maintained in liquid form at moderate temperatures and without degradation of THPA. These and other objects and advantages of the present invention will be obvious from the following discussion.